The internal elastic lamina of resistance arteries facilitates vasodilation

In large conduit arteries, smooth muscle cell elastin produces elastic laminae, while in resistance arteries endothelial cell derived elastin is the major contributor to the internal elastic lamina (IEL). The IEL in resistance arteries separates smooth muscle and endothelium and contain distinct holes in the IEL (HIEL) where the two cell types communicate via a structure termed the myoendothelial junction (MEJ). The MEJ is an anatomical hallmark of resistance arteries that pierces through the IEL and facilitates vasodilation by movement of endothelial derived hyperpolarization (EDH) to smooth muscle. In contrast, large arteries dilate via nitric oxide (NO) and do not contain MEJs. To study the role of the IEL in resistance arteries in facilitating MEJ formation and EDH-based vasodilation, we used a mouse with a Cdh5Cre to constitutively knockout elastin from endothelial cells (elastin ECKO). In en face preparations from third order mesenteric arteries, elastin ECKO mice had a 55.49% reduction in IEL surface area, and, importantly, completely lacked the distinct HIEL where MEJs could form. Regardless of this, en face claudin-5 staining demonstrated a normal endothelial cell morphology. The lack of distinct HIEL, the canonical MEJ sites, led us to hypothesize vasodilatory mechanisms may be disrupted. To test this hypothesis, we first performed pressure myography on third order mesenteric arteries from elastin ECKO mice. Myogenic tone began to diverge from littermate controls starting at 80 mmHg, with preserved active, but not passive tone. For this reason, to test for changes in EDH between control and elastin ECKO, we used arteries pressurized to 60 mmHg and performed acetylcholine (Ach) dose-response curves. We found elastin ECKO mice have decreased responses to Ach. Additionally, in the presence of 30 uM L-NAME, the majority of dilation in elastin ECKO arteries was inhibited, compared to no inhibition with L-NAME in the littermate controls. This indicated that NO-mediated dilation was present in elastin ECKO mice and not littermate controls. En face immunohistochemistry demonstrated disruption of proteins localized to MEJs that regulate EDH in resistance arteries: both phosphatidylserine (See Abstract ID:R5515) and alpha globin, which is used to chelate NO. These results indicated that the disruption in the IEL, and thus canonical MEJ sites, affected the polarization of EDH-associated proteins in the endothelium, supporting the observation of increased NO-based signaling in elastin ECKO arteries. Overall, these data imply endothelial-derived elastin is necessary for the functional formation of MEJs, the vasodilatory capacity of the endothelium, and the pathway of vasodilation in resistance arteries. © FASEB.